The best mattress protectors are the unsung heroes of the bedroom — coffee in bed becomes a much riskier prospect without one. So when it comes to keeping your mattress safe from spills and stains, is it better to save or splurge on a waterproof mattress protector?First things first: a mattress protector is a non-negotiable. When liquids get into your mattress they can cause the materials to degrade, as well as potentially supporting mold growth. If you've bought the best mattress for your sleep needs, you need to keep it safe.But before you splash the cash on a luxury mattress protector, we did some splashing of our own. I poured water, coffee, wine and other liquids on a $119 Purple Mattress Protector and a $21 Linenspa Mattress Encasement to see which kept our mattress sparkling clean. Here's the one I trust with my Sunday evening Syrah...Meet the mattress protectorsHow we tested our mattress protectorsWe wanted to put our mattress protectors through the wringer: how would they cope if a very clumsy person had a feast in bed?To do this, we wrapped each protector around a white mattress (to better show stains). We then tossed a variety of substances onto them both. Primarily liquids, we also tried some heavier, oiler substances as well — hand lotion and guacamole.Each substance was left for five minutes, to give it time to soak in. We then blotted any excess and lifted the mattress protector to see what lay beneath. In other words, was there any seepage?Finally, we washed the mattress protectors to see how easily each stain was lifted.Get instant access to breaking news, the hottest reviews, great deals and helpful tips.Test 1: Hand lotionGreasy skincare can leave mattress stains, plus it's a nightmare to clean up. We rubbed a blob of hand lotion into our protectors to see what happens...